Canvas is semi-waterproof. For the first few times the cotton fibres get wet they swell up and block the water from pouring through. But cotton dries very slowly, it's susceptible to mould and mildew, and will be damaged by repeated exposure to UV light from the sun.
For those reasons new cotton tents are treated to protect them, and should be routinely re-treated to prolong their life.
The tent I have just bought is 8 years old and covered in black mildew stains. Even so, when I spray water onto the canvas it still beads most places. That's a good sign - meaning that although the mildew will have affected the fabric, I know that destruction has been inhibited by the existing protective treatments.
For those reasons new cotton tents are treated to protect them, and should be routinely re-treated to prolong their life.
The tent I have just bought is 8 years old and covered in black mildew stains. Even so, when I spray water onto the canvas it still beads most places. That's a good sign - meaning that although the mildew will have affected the fabric, I know that destruction has been inhibited by the existing protective treatments.
Cleaning the canvas to get rid of mildew will remove much of the protection, so after I've cleaned it I'll need to re-treat it to improve the waterproofing and protect the tent for the future.
It's time for some maths.
*Marks may appear on fabric if excess product is not wiped away. Test on a hidden area first.
Use approximately 50ml of product, prior to dilution, per 3m² of fabric. The coverage is approximate and depends on the condition of the fabric being treated.
Durable Water Repellent (DWR) will develop once the fabric is dry. Allow item(s) to dry fully before packing away.
Protecting the Tent
According Zoe from Soulpad (who has been very encouraging and helpful with this project) they use Fabsil, but recommend either Fabsil or Nikwax. Fabsil don't deliver to Northern Ireland - Probably not really their fault; Royal Mail have started restricting what they'll ship across the water. Nikwax, on the other hand, sell a product called Cotton-Proof and it's readily available here. Also, Nikwax have an online web quiz that you can complete every two months to receive free samples of their products - and I don't ever ignore that level of goodwill, so I'm going with Nikwax.
How Much Nikwax do I need?
According to the instructions 50ml of undiluted Cotton Proof will treat (after dilution) 3m² fabric.
It's time for some maths.
I'll separate the tent into two parts. Walls, and Roof.
Walls
According to the diagram, the walls are 0.6m high, with a radius of 2m. .
The total area of fabric in the walls will be around 7.5m²
I've put the calculations at the bottom of the post
Roof
The roof has the same 2m radius and the total tent height is 2.5m, so if I subtract the 0.6m walls the roof is a sort of cone 4m across and 1.9m high.
That makes the area of fabric in the roof about 30m²
That's approximately 37.5m² of canvas that needs to be treated.
If 50ml of undiluted Cotton Proof treats 3m² fabric we'll need about 625ml to treat the whole tent. To be on the safe side, I'll use a one litre bottle..
That's a lot less than I thought I'd need.
Method
Nikwax Cotton Proof needs to be diluted before use.
For best results always clean item(s) first with Nikwax® Tech Wash®. No need to dry item(s) before waterproofing. Shake well before use.
Use gloves (to avoid waterproofing your hands!).
Use gloves (to avoid waterproofing your hands!).
- Erect tent OR protect working surface and lay clean item flat.
- Add 1 part product to 9 parts water and mix well.
- Apply diluted product evenly to outside of wet or dry fabric with a brush or sponge (ensure product penetrates fabric surface). For large items apply in sections.
- As you treat the fabric, remove any surplus product with a damp cloth.
- Check carefully to ensure no areas have been missed.
- After several minutes check for and remove surplus product with a damp cloth*.
*Marks may appear on fabric if excess product is not wiped away. Test on a hidden area first.
Use approximately 50ml of product, prior to dilution, per 3m² of fabric. The coverage is approximate and depends on the condition of the fabric being treated.
Durable Water Repellent (DWR) will develop once the fabric is dry. Allow item(s) to dry fully before packing away.
Maths:
the area of the walls is:
Length L=2πr
= 2 * π * 2m = 12.6m
then we multiply that by the height to get the total area of the fabric:
12.6m*0.6m = 7.6m²
The area of the roof (a cone):
m²
A=
πrl
+
π
r
2
l=
r
2
+
h
2
Solving for A
A=
πr(
r+
h
2
+
r
2
)
=
π·2·(
2+
1.9
2
+
2
2
)
≈
29.89931
Total area:
7.6+29.9 = 37.5m²
Total volume of waterproofing fluid:
37.5/3 = 12.5
12.5*50 = 625ml
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